Enhanced membrane rigidity in charged lamellar phases

Lamellar phases formed by amphiphilic molecules consist of a stack of alternating solvent layers and surfactant membranes. The stability of the structure is governed by the interactions between neighboring membranes mediated by the solvent layers, these interactions include the Van der Waals attractive forces, the hydration forces and the electrostatic forces. It was argued by Helfrich [1] that due to the very low surface tensions, the out-of-plane undulations of the membrane are important and induce a repulsion of entropic origin between membranes. The strength of the undulation repulsion is controlled by the bending elasticity of the membranes that is usually described, by the bending constants kc and kc for the mean and Gaussian curvatures.